Yesterday’s Sotheby’s ‘Magnificent Jewels and Jadeite’ sale in Hong Kong featured an exceptional blue diamond which sold for just over £4.2 million.

The 5.16 carat diamond is one of an exceptional and unique set of 12 rare blue diamonds presented to the world in 1999 by De Beers.

The centrepiece of the De Beers Millennium Jewels Collection was the ‘Millennium Star’ – a D colour, Flawless 203.03 carat pear-shape diamond which was cut from a 777 carat rough stone in a cutting process which took three years and encompassed the diamond centres of Antwerp, South Africa, and New York.

De Beers’ Harry Oppenheimer remarked that the Millennium Star was the most beautiful diamond he had ever seen.

The Millennium Collection, including the Millennium Star and this 5.16 carat diamond, gained considerable notoriety in November 2000 when a gang of jewel theives attempted to steal the whole lot by smashing a JCB digger through the gates of London’s Millennium Dome.

But De Beers and Scotland Yard were prepared for them: the diamonds had been switched for crystal replicas and police were lying in wait for the gang. Had the jewel heist succeeded, it would have been the world’s most valuable robbery, with reports at the time valuing the collection at £350 million.

Yesterday’s sale in Hong Kong featured just one diamond from this exceptional collection: a 5.16 carat blue diamond described by Sotheby’s as an ‘Important and Rare Vivid Blue Diamond‘, set in a ring flanked by two white diamonds (pictured, right).

In a supplementary catalogue note, Sotheby’s state that the diamond is ‘Accompanied by GIA report numbered 1112874424, dated 23 March 2010, stating that the 5.16 carat diamond is natural, Fancy Vivid Blue colour, Internally Flawless clarity, inscribed with “De Beers Millennium Jewel 11″.’

The auctioneer adds that the ring is size 5½ and that it was previously property from an important private collection.

Although the auction took place in Hong Kong, reflecting the current appetite of the Chinese market for collectibles such as important works of art and diamonds, the buyer of the diamond was actually reported to be Alisa Moussaieff, founder of London-based Moussaieff Jewellers Ltd, with boutiques in Bond Street, Park Lane, and Geneva.

Moussaieff is expected to re-mount the diamond in London and then offer it for sale to “discerning clients, possibly in Asia”. Some reports suggested that Moussaieff considers that she’s got a bargain, paying around $1.25 million per carat for a diamond that could fetch $2m or even $3m per carat when sold on by a renown jeweller such as Moussaieff.

In any event, the diamond ring fetched more than Sotheby’s anticipated: their pre-sale estimate for this lot was 36-46 million Hong Kong dollars, but the actual price achieved, including buyer’s premium, was 49.94 million Hong Kong dollars.